1. Field of the Invention
This invention directs itself to a method for bulk separation of single-walled tubular fullerenes based on chirality. More in particular, the present invention is directed to a method for bulk separation of single-walled tubular fullerenes utilizing a template for adsorbing single-walled tubular fullerenes of a predetermined chirality. Still further, the present invention is directed to a method of bulk separation which takes advantage of a phenomenon wherein tubular fullerenes self-orient on a similar, but planar lattice structure in an angular orientation which varies as a function of the chirality of the tubular fullerene.
2. Prior Art
Tubular fullerenes and, in particular, carbon nanotubes are of great interest because of their unique electrical and mechanical properties for use in constructing nanoscale electronic circuitry and mechanical devices. It has been discovered that the electrical properties of a carbon nanotube vary as a function of its chirality, the angle at which the graphitic lattice spirals about the tubular contour of the nanotube. Electrical properties of carbon nanotubes can vary between metallic, highly conductive structures and those which are semiconducting. One of the major hurdles to commercial utilization of these unique structures has been the problem of synthesizing the structures in a desired chirality. Currently, the synthesis of carbon nanotubes produces a mixture of chiralities. Separating nanotubes of a desired chirality from all those produced has required a very tedious and inefficient mechanical separation process utilizing a nanoprobe (e.g., an atomic force microscope). Thus, even for laboratory use, separation of a desired chirality from all those which are produced is a painstakingly slow process.
One recent approach which permits the selective preservation of the semiconducting types of nanotubes in bundles, or xe2x80x9cropes,xe2x80x9d of aligned single-walled carbon nanotubes has been demonstrated by IBM Corp. In that method, ropes of nanotubes of random chiralities are deposited on a silicon wafer that is then covered by a dense array of source, drain and gate connections in order to form field-effect devices. Subsequently, a voltage is applied over the nanotube ropes blowing out and destroying the metallic tubes, but leaving the semiconducting type unscathed. Thus, the surviving semiconducting nanotubes are available and still affixed as ropes to the contacts, where they may be utilized to produce active devices. However, the method provides no means of physically segregating or sorting the nanotubes into separate assemblies or containers. Nor does it provide a means for accumulating the highly conductive nanotubes. More importantly, this approach does not apply at all to the problem of sorting the nanotubes according to their chiral structure.
Whereas in the invention of the subject Patent Application a method is provided where either semiconducting or highly conductive nanotubes can be physically sorted or separated in bulk quantities from the typical mixture of nanotube types synthesized by current methods, which thus provides advantages over the prior art methods. Still further, the method of the invention of the subject Patent Application is far simpler to implement than prior art methods.
A method for bulk separation of single-walled tubular fullerenes based on chirality, is provided. The method includes the steps of:
a. forming a template on a crystalline substrate having a plurality of openings oriented to energetically favor adsorption of a respective plurality of single-walled fullerenes having a tubular contour and a selected chirality;
b. exposing the template to a suspension of single-walled tubular fullerenes of random chiralities for adsorption of single-walled tubular fullerenes of the selected chiralities into the openings of the template;
c. removing the template from the suspension; and,
d. removing the adsorbed single-walled tubular fullerenes of the selected chirality from the template.
In order to form the template, a crystalline substrate is provided which has a predetermined lattice structure. Then, a plurality of single-walled tubular fullerenes of the selected chirality are deposited on the substrate. The deposited single-walled tubular fullerenes have a lattice structure that is disposed in aligned relationship with the predetermined lattice structure of the crystalline substrate. Next, exposed areas of the crystalline substrate surrounding each of the single-walled tubular fullerenes are coated with a composition having a greater affinity for the crystalline substrate than for the single-walled tubular fullerenes of the selected chirality. Lastly, the single-walled tubular fullerenes that had been deposited on the substrate are removed, leaving the composition coating the substrate undisturbed with elongated openings that define a template for the subsequent adsorption, onto the substrate within the openings, of tubular fullerenes having the same chirality as that of the tubular fullerenes utilized to form the template.
From another aspect, a method for bulk separation of single-walled tubular fullerenes based on chirality is provided, which method includes the steps of:
a. providing a crystalline substrate having a predetermined lattice structure;
b depositing a plurality of single-walled tubular fullerenes of a selected chirality on the substrate, the deposited single-walled tubular fullerenes having a lattice structure thereof in aligned relationship with the predetermined lattice structure of the crystalline substrate;
c. depositing a layer of molecules on the crystalline substrate surrounding each of the single-walled tubular fullerenes of the selected chirality, the molecules being of a composition having a greater affinity for the substrate than for the single-walled tubular fullerenes of the selected chirality;
d. removing the single-walled tubular fullerenes from the crystalline substrate to form a template without disturbing the layer of molecules;
e. exposing the template to a suspension of single-walled tubular fullerenes of random chiralities for adsorption thereon of single-walled tubular fullerenes of the selected chirality;
f. removing the template from the suspension;
g. exposing the template to a solvent solution for removing the adsorbed single-walled tubular fullerenes therefrom; and,
h. recovering the single-walled tubular fullerenes of the selected chirality from the solvent solution.